1. Field of the Invention
The present invention relates to a transformer-based oscillator, and more specifically, to a transformer-based oscillator suited to oscillate frequencies in multiple bands.
2. Discussion of Related Art
A voltage control oscillator (VCO) is kind of an oscillator and control a voltage to vary the capacitance of a variable capacitor (or varactor) so as to control a frequency. The VCO may be widely employed for wired/wireless communications transceivers.
In recent years, with technical developments of tuners, SDRs, and multiband receivers, a vast amount of research has been conducted on wide-band VCOs configured to improve phase-noise performance.
Although LC-tank VCOs have mainly been used conventionally, the LC-tank VCOs may have low noise performances, and the number of capacitors or varactors constituting tanks cannot be increased within wide ranges in fixed frequency ranges. In other words, the conventional LC-tank VCOs may be inappropriate for the output of broadband frequencies.
To solve the above-described problem, a technique using a switch-controlled inductor and a technique using a switch capacitor array have been proposed.
The technique using a switch-controlled inductor may include connecting a switch to an inductor to control the entire inductance using a switch so that a resonance-frequency output range of a VCO can be increased. Also, the technique using a switch capacitor array may include outputting a wide-band frequency using a fixed capacitance varied by a varactor and a plurality of binary controllers.
However, in the technique using the switch-controller inductor, an inductance may be controlled using a switch, and thus the characteristics of the inductor can be degraded, deteriorating the performance of the VCO. Also, in the switch capacitor array technique, since a switch-controlled capacitor may include a control device having a parasitic component and the Q-factor of a resonance unit may be reduced due to a channel resistance of a switch transistor, the switch capacitor array may have degraded phase noise characteristics.